1. Field of the Invention
The present invention relates to electronic equipment having a memory.
2. Related Background Art
In a prior art electronic equipment of this type, there may be a risk that data stored in a RAM is destroyed because the RAM is normally in a writable state. Causes of data destruction are static electricity, malfunction due to external noise, and programming overrun of a processor such as a CPU which processes the data stored in the RAM. For example, in a facsimile machine, power is turned on 24 hours a day and the chance of data destruction is high. The data may also be destroyed by a malfunction due to electrostatic noise generated by a paper feed.
The necessity of modifying the data stored in the RAM is very little in normal operation, except when the RAM is used as a register, and in many cases it is read-only. Such a RAM may be substituted by a ROM, but when a ROM is used, a modification of data at a customer site is not possible. Such modification of the data is required, for example, in a highly intelligent facsimile machine, to store information peculiar to the customer, such as telephone numbers of senders and senders. If a rewritable ROM (EEPROM) is used instead of the ROM, the rewriting on site is attained but it is relatively expensive and has problems in durability and reliability.